1. Field of the Invention
This invention relates to a capping mechanism, and more particularly to a capping mechanism adapted to effect the operation for recovering discharge function by causing negative pressure suction relative to the orifice portion of a liquid injection recording apparatus for discharging liquid as flying droplets.
2. Description of the Prior Art
The liquid injection recording apparatus is a recording apparatus in which a pressure corresponding to a recording signal is applied to liquid such as ink filling a liquid flow path and the liquid is discharged as liquid droplets from orifices formed at the fore end of the liquid flow path, thereby effecting dot recording on a recording medium, and is also called an ink jet printer.
In the liquid injection recording apparatus of this type, when a mechanical shock or a sudden temperature change is imparted to a recording head formed with one or more orifices, air enters the flow path or solvent gases are produced in the liquid to destroy normal meniscus, whereby discharge of liquid droplets ar not effected in conformity with the recording signal or, if discharged, the liquid droplets are further dispersed as splash or satellite, thereby causing unsatisfactory printing.
To recover the apparatus from such unsatisfactory discharge or unsatisfactory printing, there is provided a discharge recovering mechanism for sucking ink from the orifice side by a negative pressure and recovering normal meniscus.
This discharge recovering mechanism is called a capping device and is provided, for example, at the home position of the recording head. The discharge recovering mechanism is provided with an elastic cap adapted to be brought into intimate contact with an orifice surface when the recording head has returned to its home position, and this cap is urged against the orifice surface to effect moderate negative pressure suction and suck liquid from the orifice portion, thereby forming meniscus at a normal position.
An example of the construction of the discharge recovering mechanism of this type according to the prior art is schematically shown in FIGS. 1 to 3 of the accompanying drawings.
In these Figures, reference numeral 1 designates a recording head unit having at the rear thereof a sub-tank provided on a carriage, not shown. A plurality of orifices 2 are formed in the fore end portion of the recording head unit 1. The orifices 2 provided in the fore end portion need not always be plural, but a single such orifice may be provided there.
Liquid such as ink is always supplied from a main tank, not shown, into the sub-tank of the recording head unit 1 so that the liquid can always be supplied into a liquid flow path provided between the orifices 2 and the sub-tank.
On the other hand, a capping device is provided on the fixed portion side of the apparatus. This capping device has a cap 3 in which an elastic member 4 is contained. A recess 7 is formed in the fore end portion of the elastic member 4 and is connected to a negative pressure suction pump 6 through a tube 5.
To effect the operation for recovering the discharge function under the above-described construction, the cap 3 is advanced with the orifices 2 being opposed to the cap 3, the elastic member 4 is urged so as to surround all the orifices 2, and the negative pressure suction pump 6 is operated to render the interior of the recess 7 into a negative pressure state through the tube 5 and effect the suction of the liquid from the orifices 2.
By such operation, the meniscus too much retracted recovers its normal position as previously described, whereby normal recording can be accomplished.
However, the adoption of the capping device which is the discharge recovering mechanism of the above-described structure using a negative pressure leads to the following disadvantages.
The cap 3 is brought into intimate contact with the orifice surface so as to surround the orifices 2 to thereby effect capping and negative pressure suction, whereafter when the cap is open, the sucked ink 8 is in the recess 7 as shown in FIG. 2 and therefore is pulled toward the orifices 2 and toward the elastic member 4 by surface tension. As a result, an ink pool 9a is created on the orifice side and an ink pool 9b swelling out from the elastic member 4 is created on the cap side.
As a result, the ink pool 9a on the orifice side covers the orifices 2 as shown in FIG. 3 and thus causes unsatisfactory discharge, and the ink pool 9b on the cap side swelling out from the elastic member 4 contaminates the surroundings of the cap and by a number of recovering operations, the contamination spreads toward the carriage for sliding the sub-tank.
Such a phenomenon makes it difficult to retain the liquid because the area of the opening of the recess 7 of the elastic member 4 is very great in a recording head of the multi-orifice type, and thus the inconvenience resulting from the liquid pools occurs more often.